1. Field of the Invention
The present invention relates to an antenna, a radio receiver, and a method for manufacturing the antenna.
2. Description of the Related Art
Conventionally, there is known a radio receiver, such as a radio controlled timepiece, including an antenna which receives standard radio waves including time information. The radio receiver automatically corrects a current time on the basis of the time information.
As the antenna, which receives standard radio waves, of a radio controlled timepiece as an example of a radio receiver, there is an antenna often used, the antenna being constituted of a core made of a magnetic material sensitive to radio waves, such as an amorphous metal or ferrite, and a coil winding around the core.
In a case where a radio receiver is a radio controlled watch, in order to, for example, make the radio controlled watch sumptuous or improve design or durability of the radio controlled watch, a metal member may be used as an antenna case in which an antenna is housed, a cover of the antenna case, or the like.
In this case, namely, in the case where a metal member is used in a radio receiver, if an antenna is disposed near the metal member, the so-called eddy current is induced, and loss is caused thereby, which leads to decrease of sensitivity of the antenna to standard radio waves.
To deal with the problem, in Japanese Patent Application Laid-Open Publication No. 2006-81140, it is proposed, as a configuration of an antenna to prevent the sensitivity of the antenna from decreasing even if no enough distance can be secured between a metal member and the antenna, to dispose a gap-provided secondary magnetic path member on apart of a core in an magnetic sensor-type antenna having a primary magnetic path member constituted of (i) the core (magnetic core) made of a magnetic substance and (ii) a coil winding around the core, and receiving magnetic-filed components of electromagnetic waves with the primary magnetic path member.
However, in the antenna disclosed in Japanese Patent Application Laid-Open Publication No. 2006-81140, the member constituting the secondary magnetic path where a coil does not exist is disposed in such a way as to contact the member constituting the primary magnetic path where a coil exists, and magnetic flux entering the antenna from outside branches and flows into (passes through) the primary magnetic path and the secondary magnetic path. The magnetic flux flowing into the secondary magnetic path where a coil does not exist becomes loss, and the sensitivity of the antenna decreases.